The rich keep getting richer — here are the billionaires who made the most billions in a single year

With a record number of billionaires around the world, we calculated just how much the world's richest billionaires earned in a single year.

According to our calculations, Bill Gates earned $4 billion, making him the lowest-earning billionaire on the list — nothing compared to Jeff Bezos' annual earnings of nearly $40 billion.

The rich keep getting richer. If there's one thing that can be said for billionaires, it's that they know how to grow their wealth.

According to Wealth-X's 2018 Billionaire Census, there are a record number of billionaires around the world, and their wealth has increased by 24% since last year — another record number.

Business Insider looked at how much the world's richest billionaires earned in the past year. To determine each billionaire's annual earnings, we calculated the difference between their 2017 and 2018 net worths for the top 50 richest billionaires, as provided by the Forbes' 2017 and 2018 richest people in the world lists, published every March. We then narrowed the rankings down to the top 30 billionaires who made the most money in the past year.

We didn't include Francois Bettencourt and Giovanni Ferrero because they inherited their billions in the last year.

The lowest-earning billionaire on the list, Bill Gates, earned $4 billion. While that's far from a measly number, it doesn't compare to the nearly $40 billion Jeff Bezos earned in the past year.

Below, see how many billions some of the world's richest billionaires earned in a single year.